# Can Light Speed Be Slowed to 38mph? | Harvard Gazette

• bayan
In summary, a group of scientists was able to slow down the speed of light to almost 38mph by reaching almost Absolute zero. This sparked a discussion about whether this meant that 38mph was the minimal universal speed limit. However, it was later discovered that the same group was able to completely halt light at 0m/s, disproving the idea of a minimal universal speed limit. The experiment involved compressing the light pulse by a factor of ten million and imprinting a phase grating in the atom cloud. It was also noted that the concept of a photon being fundamental was challenged, as the compressed pulse contained only 1/400th of the energy of a free-space photon. There were also discussions about grammatical errors in
bayan
In an article which I had read last year about a couple of scientists slowing the speed of light to almost 38mph by reaching almost Absloute zero.

since the speed of light in a vacuum is the maximum universal speed limit, would this mean that 38mph is the minimal universal speed limit?

if this Idea is wrong can someone please give reasons why it is wrong so I can understand and hopefuly learn from my mistakes

Oh incase anyone wants to read the article here is a link

http://www.news.harvard.edu/gazette/1999/02.18/light.html

Well its wrong because I know about a million things that go slower than 38 mph, as to why its wrong I'm sure you will get better answers from someone else. But it's not just the super cold temperature that makes the light slow down by itself for starters.

Last edited:
bayan said:
In an article which I had read last year about a couple of scientists slowing the speed of light to almost 38mph by reaching almost Absloute zero.

since the speed of light in a vacuum is the maximum universal speed limit, would this mean that 38mph is the minimal universal speed limit?

if this Idea is wrong can someone please give reasons why it is wrong so I can understand and hopefuly learn from my mistakes

Oh incase anyone wants to read the article here is a link

http://www.news.harvard.edu/gazette/1999/02.18/light.html

You are several years too late. The same group headed by Lena Hau has managed to "halt" light completely, i.e. 0 m/s.[1] So there is no "minimal unversal speed limit", at least not from this.

Zz

[1] C. Liu et al., Nature v.409, p.490 (2001).

Would 38mph have been the 'maximum universal speed limit' in the ~0K conditions? For those of us who don't have access to journals, can you summarize the experiment?

whozum said:
Would 38mph have been the 'maximum universal speed limit' in the ~0K conditions? For those of us who don't have access to journals, can you summarize the experiment?

http://physicsweb.org/articles/world/14/9/8/1

Zz.

What happens when the light pulse slows down is that it is compressed by a factor of some ten million, leaving an almost negligible amount of energy in the pulse. (In free space the pulse contains 25 000 photons and, once compressed, it contains only 1/400 of a free-space photon.) When we turn the coupling laser off abruptly, the light pulse comes to a grinding halt, and the atoms within the localized pulse region are left in their superposition "dark states". In these states, the relative proportions of states 1 and 2 is a measure of the electric-field ratio between the light pulse and the coupling laser before turn off. In effect, we imprint a phase grating in the atom cloud as if we were recording a hologram.

I thought the photon was fundamental? How can there be 1/400th of a photon?

whozum said:
I thought the photon was fundamental? How can there be 1/400th of a photon?

It's 1/400th of 25,000 free-space photons!

Zz.

Am I misunderstanding or did they make a critical grammatical error?

seems like I am several years back :) hah. had not read about them being able to stop it.

## 1. Is it possible to slow down the speed of light to 38mph?

No, it is not possible to slow down the speed of light to 38mph. The speed of light in a vacuum is a fundamental constant of the universe and cannot be altered. It is approximately 186,282 miles per second, or 670,616,629 miles per hour.

## 2. Why is the speed of light considered the maximum speed?

The speed of light is considered the maximum speed because it is the fastest speed at which all matter and information can travel in the universe. This is due to the laws of physics, specifically Einstein's theory of relativity.

## 3. Can anything travel faster than the speed of light?

No, according to our current understanding of physics, nothing can travel faster than the speed of light. As an object approaches the speed of light, its mass increases exponentially, making it impossible to reach the speed of light itself.

## 4. How is the speed of light measured?

The speed of light is measured by using precise instruments and experiments, such as the Michelson-Morley experiment and the modern technique of using lasers and mirrors to measure the time it takes for light to travel a known distance. These measurements have consistently confirmed the speed of light to be 299,792,458 meters per second.

## 5. Can the speed of light be exceeded in certain mediums?

Yes, the speed of light can be exceeded in certain mediums, such as water or glass. This is due to the fact that light travels at different speeds in different materials, based on their refractive index. However, this does not mean that the speed of light in a vacuum can be exceeded.

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